Traditional holographic films typically are made by a procedure summarized as follows. A substrate (such as an acrylic coated oriented polyester film) is coated with an embossable coating. This film is then passed across an etched roller under heat and pressure to emboss the coating. Typical embossment depths are a few angstroms to about 2 mils. A clear high refractive index material (typically indium tin oxide or zinc sulfide) or a metal (often aluminum) is applied to the embossed side to preserve the image integrity. Such holographic decorative films are commercially available under the trademark SPECTRATEK®, of Spectratek Technologies, Inc., as are other products from other sources. When desired, these can be available in the art without the high refractive index (HRI) material or aluminum having been applied to the embossed surface.
It will be appreciated in the art that these types of traditional holographic films essentially are films that have been embossed. Often in the art, a holographic embossed film includes at least one layer that reflects light at an angle different from other panels or portions of the surface having the embossment. These films can be said to have diffractive optical elements, jagged etch cuts, image-imparting prismal etching, micro-angled cuts, or prismal or holographic style effects. Such elements often give the embossed film refractive characteristics that typically vary with the angle and wave length of the light emitted onto the embossed surface. The terms holographic and embossed, when used herein, signify a surface that has embossed members or facets. While these embossed films or surfaces can exhibit the diffractive optical elements that often are labeled as holographic, a strict definition of holographic is not intended. Instead, such term refers to surfaces or films that have differing depth characteristics, that is they are embossed, whether or not the reflective angles are such as to fall within a strict definition of holographic.
Over the years, embossment approaches have been used to provide or enhance decorative and/or functional polymer film surfaces. These can include embossments that have strict holographic properties which often are considered desirable due to their unique and eye appealing and interest-generating aspects. Often, it is essential that such products exhibit an eye-catching character that can be imparted by high refractive index (HRI) materials by adding the materials or metals discussed above and that typically are applied as a clear or transparent layer onto the embossed areas of the film. While this is often successful in preserving image quality and surface integrity, it has come to be appreciated that holograms made in the traditional way described hereinabove are susceptible to weaknesses that can be manifested when such embossed films are to be included on products that are expected to be used under rugged conditions. Typical holographic or embossed films are not durable when subjected to harsh environmental conditions, particularly including repeated and forceful physical contact with rigid items, which often involves kinetic energy transfer upon contact between the holographic surface and such an item. These can take the form of impacts from rigid objects hurled onto the surface or objects that, due to the nature of the holographically decorated product constantly engage and impart forces into the surface.
Weaknesses in these instances can include the following. HRI coatings and adhesive layers used in such traditional holographic films can exhibit low thermal stability, making them vulnerable to higher processing temperatures and to environmental degradation, such as would be encountered in outdoor use. In addition, material breaks occur at interfaces, particularly when overlayer barriers are used when the product is intended for rugged applications. Metallized top layers, for example, which can also impart added reflectance and a metallic look, can experience breaks due to relatively weak bonds at layer interfaces. Particularly problematic in this regard are material breaks at interfaces between metallized layers and layers of other materials or films.
Accordingly, in the art, it is generally understood that decorative embossings and holograms cannot be used on products that are intended for rugged end use. This is because the holograms will split apart and compromise the construction of the product. The art would generally believe that standard hologram approaches would split if the material were exposed to situations under which substantial stress and/or impact is imparted repeatedly. Accordingly, there is a need for an approach that addresses these concerns and provides a durable approach for applying decorative embossed surfaces onto products that will avoid these types of splitting and separation concerns.
Often, it is further desired that decorative surfaces that have holographic or embossed characteristics also have images applied to the surface. Typically, images would be applied by printing, inking or dyeing techniques. One problem that is recognized with holographic or embossed surfaces is that many printing, inking and dyeing techniques obscure the embossed or holographic effect. It is believed that this can be caused by the inking media filling several or all of the embossment depressions. This can be referred to as “wetting out” or “clearing” the holographic imagery. It will be appreciated that filling or coating some or all of the depressions changes the reflectance of the hologram or embossment. Conventional printing techniques, such as those using conventional inks include offset, flexographic and lithographic technologies, experience this “wetting out.”
While it has been generally appreciated that dye sublimation imprinting is a useful means of direct image transfer, prior publications such as Flaherty, U.S. Patent Publication No. 2004/0143914 do not teach how to use dye sublimation technology in a manner that is suitable for low-cost rugged use. For example, the Flaherty publication describes a laminate having a frangible hologram embedded therein, while providing a surface that is receptive to dye sublimation direct image transfer.
Benton et al., U.S. Pat. No. 6,632,507 discusses holographically enhanced decorative laminates, teaching heat and pressure embossing lamination. This describes a laminate sheet assembly having a polypropylene-based release sheet that, upon the application of heat and pressure, transfers a holographic image onto an overlay layer of the laminate for application to a rigid substrate such as plywood, particle board, chip board and medium density fiberboard. By this approach, the polypropylene-based sheet containing the holographic image functions as a release sheet for conventional decorative laminate lay-ups having the overlay layer, a pattern layer and a core layer which is composed of one or more layers of phenolic resin impregnated craft paper. The overlay layer is said to include aluminum oxide for wear resistance. While this patent is intended for application to rigid substrates and for rugged use such as countertops, flooring panels and wall panels, this is accomplished in a somewhat traditional manner of using laminate sheet assembly onto which a holographic image is impressed by heat and pressure into an overlay layer to which a wear coating is applied after the holographic image is formed thereon.
Another approach which incorporates transfer of physical embossment of a holographic image is illustrated by Stepanek, U.S. Pat. No. 5,900,095. This encompasses, for example, a transfer of a holographic image from a polymeric support to a tissue paper substrate. This patent and all other patents, references and publications identified herein are incorporated hereinto by reference.
Prior approaches such as these require somewhat complicated means for imparting embossed or holographic images. While some of this art discusses relatively rugged uses, this can increase complexity according to the solutions given by this prior art. They are also not described as being particularly well suited for combining holographic technology with printing, inking or dying in order to impart indicia, wording, images or other decorative or informative elements, typically when combined with multiple color displays. Accordingly, the art does not provide an approach by which holographic features can be employed in a low-cost manner that is advantageously straight forward and is well-suited to rugged uses including for recreational sportsboards, as well as other uses where simplicity and durability are assets. Further needs are appreciated where one wishes to combine a holographic or embossed feature with a printing, inking or dying feature, particularly one in which the holographic type feature and the additional decorative features are simultaneously visible on the product.